The present disclosure relates to a headphone device for use in noise-canceling headphones.
A noise-canceling headphone, which, in a noisy environment, reproduces audio signals with sufficiently reduced noise, has been known. Noise-canceling processing is performed on each channel. Noise-canceling headphone devices in related art had a noise-canceling processing circuit housed in the respective housings of the left and right channels.
In addition, in recent years, as described in JP 2008-122729 A, digital noise-canceling having a digitized noise-canceling function has been put into practical use. The digital noise-canceling is a method which digitizes noise detected by a built-in microphone of the headphone and implements signal processing, thereby generating sound in antiphase that has an effect of canceling the noise so as to reduce the noise. Compared to the analog noise-canceling method, the digital noise-canceling method can generate noise-canceling signals of high accuracy by means of digital noise-canceling software.
Typically, the digital noise-canceling processing unit uses a digital signal processor (hereinafter referred to as “DSP”) and includes an integrated circuit (hereinafter referred to as “IC”). Thanks to the processing capability and processing speed of the DSP, it is possible to implement two-channel noise cancelation processing. In this case, the noise-canceling processing unit can be disposed in the housing of one of the two channels, for example, the left channel (hereinafter referred to as “L-channel”) by having the left and right channels share the noise-canceling processing unit.
Between the noise-canceling processing unit and the other right channel (hereinafter referred to as “R-channel”), a signal from the microphone (referred to as “microphone signal”) installed in the vicinity of the headphone unit of the R-channel is supplied to the noise-canceling processing unit via a cable arranged along a headband. The noise-canceled audio signals of the R-channel, which are generated by the noise-canceling processing unit, are supplied to the headphone unit via a cable arranged along the headband.
In the case of the over-the-head type headphone (also referred to as “headband type headphone”), a shielded cable was typically used to transmit the microphone signals of the R-channel to the L-channel. The shielded cable includes an internal conducting wire (a single conducting wire or multiple coated conducting wires) and an external conductor (a fine conductor or metal foil) enclosing the internal conducting wire. The external conductor is regarded as being at the ground potential.